More docfixes (#1369)

Arg[z] and other scattered typos

Author: mmatera

mathics/builtin/arithmetic.py

@@ -106,7 +106,7 @@ class Arg(MPMathFunction):
     :WMA link:https://reference.wolfram.com/language/ref/Arg.html</url>)
 
     <dl>
-      <dt>'Arg'[$z$, $method_option$]
+      <dt>'Arg'[$z$, 'Method ->' "$option$"]
       <dd>returns the argument of a complex value $z$.
     </dl>
 

mathics/builtin/kernel_sessions.py

@@ -12,7 +12,7 @@ class Out(Builtin):
     <url>:WMA: https://reference.wolfram.com/language/ref/\$Out</url>
     <dl>
       <dt>'%$k$' or 'Out'[$k$]
-      <dd>gives the result of the $k$th input line.
+      <dd>gives the result of the $k$-th input line.
 
       <dt>'%'
       <dd>gives the last result.

mathics/builtin/string/operations.py

@@ -56,7 +56,7 @@ class StringDrop(Builtin):
       <dd>gives $string$ with the last $n$ characters dropped.
 
       <dt>'StringDrop'["$string$", {$n$}]
-      <dd>gives $string$ with the $n$th character dropped.
+      <dd>gives $string$ with the $n$-th character dropped.
 
       <dt>'StringDrop'["$string$", {$m$, $n$}]
       <dd>gives $string$ with the characters $m$ through $n$ dropped.